Separation of benzol from coke oven and like gases



G. MAIURI 2,219,782

SEPARATION OF BENZOL FROM COKE. OVEN AND LIKE GASES Filed Aug. 15, 1939 2 Sheets-Sheet 1 INVENTORZ Gm: no MmuRl HTTORNEI INVENTORI cTUlOO Manual a 6 HTTOIR N: y

Patented Oct. 29 1940 I SEPARATION OF BENZOL FROM COKE OVEN AND LIKE GASES Guido Maiuri, Aldwych, London, England Application August 15, 1939, Serial No. 290,202 In Great Britain August 22, 1938 8 Claims. (Ci. 62-1755) This invention relates to the separation of benzol from coke oven and like gases by condensation at. a low refrigeration temperature. The object of the invention is to efiect theseparation of the benzol without the process becoming interrupted by choking of the apparatus by the solidification of benzene and other products.

It is known that benzol can be separated from coke oven and like gases, such as town gas, by

10 cooling the gas to a temperature and under a pressure at which the benzol becomes liquefied. Owing however to the difficulty hitherto of commercially obtaining a low refrigeration temperature, the process has been carried out with gas compressed to severalatmospheres. Also the process has hitherto been effected with a refrigerating apparatus producing approximately only a single refrigerating temperature, namely the minimum temperature.

Benzene solidifies, without passing through a liquid phase, at +6 C. at atmospheric pressure, but at the low partial pressure of benzene in the gas, due to the small proportion of benzene in the gas, the benzene in the gas solidifies at much lower temperatures, of for instance -20 'C. to 60 C. With the gas at atmospheric pressure, the toluol contained in the gas starts liquefying at moderate cold temperatures, which may be as high as 10 C.

Abrupt cooling of the benzene by refrigeration applied at the minimum temperature produced by the refrigerating machine causes the benzene abruptly to crystallise out of the gas, and thereby to choke the apparatus.

Now according to the present invention, benzol is separated from coke oven and like gas by gradually cooling the gas and thereby gradually condensing the benzol by heat-exchange with a refrigerant evaporating alonga range of temperatures into an inert gas flowing in contra-flow with the coke oven or like gas. The gradual cooling enables the toluol, liquefied at a relatively high refrigerating temperature, to absorb the benzene vapour and thus prevents the deposit of benzene in the solid condition. The liquefied toluol also absorbs other vaporous constituents of the gas which would require temperatures lower than the minimum refrigerating temperature produced, in order to separate them from the gas 5 by condensation.

In other words, the gradual cooling of the gas enables the toluol, which is liquefied at the higher temperatures of the range of refrigerating temperatures, to strip the gas of the vapour of benzene and also to absorb other vapours which would otherwise remain permanently in the gas.

The solution in the liquid products of any sulphur present in coke oven or like gas is promoted by the gradual cooling, because the solvent power of these products becomes gradually in- 5 creased by the gradual decrease of temperature as the sulphur content of the gas becomes gradually decreased by the solution of the sulphur in the liquid products condensed from the gas.

The process can be carried out with the gas at 10 any suitable pressure, including at atmospheric pressure, and with a range of refrigerating temperatures of, for instance, from 30" C. to C. Such a range of temperatures can be produced by a diflusion absorption refrigerating machine as 15 described in the specification of Patent No. 2,153,020, using ammonia as the refrigerant, water as the absorbent and hydrogen as the inert gas. The coke oven orlike gas is admitted to the upper end of the coiled pipe w in the evapo- 2o rator of this machine. However, in order to avoid the frictionalresistance to flow of the coke oven or like gas, such as would occur if the gas flowed through a pipe such as the coiled pipe w, the evaporator is preferably modified in construc- 25 tion so that thisgas fiow's through a chamber instead of through a. coiled pipe.

To provide an increased amount of liquid available for absorbing the benzene and other vapours, part of the resulting'liquid products may be introduced to pass with fresh coke oven or like gas again in contra-flow heat-exchange with the evaporating refrigerant an'd inert gas in the evaporator.

Should the content of toluol of the coke oven 35 or like gas be insufiicient to absorb sufficient of the benzene, liquid toluol may be introduced with the gas. Such liquid toluol may be extracted by fractional distillation from the liquid products previously obtained.

Prior to the above. described cooling of the coke oven or like gas by contra-flow heat-exchange with the inert gas and refrigerant, the coke oven or like gas may be precooled by ascend- I ing in a heat-exchanger cooled by coke oven or 5 like gas returning from being cooled by the inert gas and refrigerant.

A plant for carrying out the invention is illustrated somewhat diagrammatically in sectional elevation on the accompanying drawings, in 50 which Figs. 1 and 1a represent the left and right halves of the complete apparatus.

a is a serpentine evaporator pipe wherein liquid refrigerant, for instance ammonia, admitted by a pipe b, evaporates in the presence of inert gas, 55

for instance hydrogen, admitted at the-bottom by a pipe 0. The inert gas together with evaporated refrigerant progressively leaves the evaporator pipe a, by pipes d d d d and :1 so that the evaporation of the refrigerant takes place into progressively less inert gas, as the partial pressure of the refrigerant in the inert gas mixture increases. This has the effect, as explained in patent specification No. 2,153,020, of maintaining the production of cold substantially constant whilst the temperature of evaporation increases under the increasing partial pressure of refrigerant, for instance from 60 C. at the bottom end to 20 C. at the top end of the evaporator pipe a. Any unevaporated refrigerant drains back to the absorber by a pipe a The generator, condenser and absorber of the refrigerating machine of which the serpentine pipe a constitutes an evaporator element, are substantially the same as those described in the specification 'of Patent No. 2,153,020, and are therefore not illustrated. The liquid refrigerant and the inert gas before entering the evaporator pipe a, are precooled by heat-exchange with inert gas and refrigerant vapour which have left the evaporator by the pipes d d d d and a The evaporator pipe a is contained in a chamber e, to the top of which coke oven or like gas is admitted, at for instance atmospheric pressure, by a pipe I. The coke oven or like gas passes down through the chamber e sweeping the evaporator pipe a, which is externally provided with heat-transmitting fins a and leaves the bottom of the chamber e, by ports e which communicate with an annular passage 9, to which is connected a pipe h.

In sweeping the evaporator pipe a, the coke oven or like gas is gradually cooled, by the refrigerant evaporating under increasing partial o pressures of refrigerant in the evaporator pipe a, and the condensible constituents in the coke oven or like gas thereby become condensed on the outside of the evaporator pipe aand drain to the bottom of the chamber e. The gradually 45 cooled and gradually condensing liquid products absorb the constituents of the coke oven or like gas, such as benzene, which otherwise would crystallise'out as solids and choke the plant, and also absorb some gaseous constituents which 50 otherwise would remain permanently as gases. Sulphur is also absorbed. The liquid products drain by a pipe. i, warmed by a water jacket i into a decanting vessel 7. The benzol decants through a pipe 7: into a ves- 55 sel k. Water decants through an overflow pipe 1 into a vessel 1 from which the water runs to waste.

Some benzol is delivered by a pump It from the vessel It, up a pipelr: to an elevated vessel k The bulk of the benzol overflows from the vessel 7: along a pipe it to a storage vessel (not shown).

The benzol in the elevated vessel It on periodically sufflciently increasing in'level periodically floods a syphon m at the upper end of a pipe m which thereby intermittently delivers the benzol to a perforated spraying pipe m? within the evaporator chamber e above the evaporator pipe a. The sprayed benzol wets the outer surface of the evaporator pipe a and its flns a and thus 70 provides additional liquid to absorb benzene and other constituents of the coke oven or like gas.

Before admission to the evaporator chamber e, the coke oven or like gas is-precooled by heatexchange with gas leaving by the pipe h.

n For this purpose the fresh coke oven or like gas, which is supplied at atmospheric temperature to the plant by a pipe 12, ascends the tubds of a tubular heat-exchanger or 0 around which the cold gas leaving the evaporator chamber e by the pipe h, descends in contra-flow. In the tubular heat-exchanger 0 or o the gas is precooled to from C. to '15 C. (the temperature depending on the water content of the gas), and the major portion of the water vapour is condensed. The condensed water in trickling down the inner surface of the heat-exchanger tubes washes down naphthalene and thus prevents it sticking to the walls of the tubes. The water by freezing gradually forms a deposit of ice within the tubes which eventually would block them. For this reason two tubular preheating heat-exchangers o and o are provided, and one is traversed and cooled by the escaping gas from the pipe h, whilst the other is traversed and warmed and the ice therein thawed by the fresh coke oven or like gas supplied by the pipe n.

The fresh coke oven or like gas supplied by the pipe 12 is, by a two-way .cock 1), diverted into either the heat-exchanger 0 or into the heatexchanger 0 to ascend within the tubes thereof and thaw any ice therein. By means of another two-way cock q at the top, the fresh gas, after having ascended in the one heat-exchanger, descends a pipe 1' to the two-way cock 9, which diverts the gas to ascend within the tubes of the other heat-exchanger. This heat-exchanger is cooled by coke oven or like gas leaving the evaporator chamber e by the pipe h and admitted into the top of the space surrounding the tubes of the respective heat-exchanger, by opening a valve is or 5 After passing through the heat-exchanger the escaping gas passes out through a pipe t or t to an outlet pipe 11..

In the drawing the heat-exchanger 0 is being thawed out by the fresh gas, whilst the heat-exchanger o is cooling the fresh gas by the gas escaping from the evaporator chamber e.

The valve s on the heat-exchanger 0 is opened and the valve s on the heat-exchanger 0 is closed, and the two-way cocks p and q are adjusted, to change over the heat-exchanger 0 to thawing and the heat-exchanger 0 to cooling. The escaping gas then flows from the heat-exchanger 0 by the pipe. t to the outlet pipe u. The heat-exchanger which is thawing out is drained by a pipe 12 or v" on opening a cock w or On starting the process and before admitting fresh coke oven or like gas to the plant, the gas inlet pipe 12. is temporarily connected to the gas outlet pipe 11., so that gas already in the pipes circulates in a closed circuit through the evaporator chamber e and through the two heat-exchangers o and o, in one inside the tubes and in .the other outside the tubes, and so cools down both heat-exchangers from atmospheric temperature to an initially sufliciently low temperature for the subsequent heat-exchange to be effective.

I claim: 1. A method of separating benzol from hydro carbon gases, consisting in precooling said hydrocarbon gases by upward contra-flow heat-exchange with escaping cooled hydrocarbon gases, evaporating a refrigeratnt under increasing partial pressures of refrigerant and over a range of,

increasing subatmospheric temperatures into inert gas, and cooling said precooled hydrocarbon gases by absorption of heat therefrom at temperatures along said range of temperatures by said inert gas and said refrigerant evaporating, thereinto under said increasing partial pressures.

2. A method of separating benzol from hydrocarbon gases, consisting in precooling said hydrocarbon gases by upward contra-flow heat-e11 change with escaping cooled hydrocarbon gases, evaporating a refrigerant under increasing partial pressures of refrigerant and over a range of increasing sub-atmospheric temperatures into inert gas, and gradually cooling said preccoled hydrocarbon gases by contrafiow heat-exchange with said inert gas with said refrigerant evaporating thereinto under said increasing partial pressures.

3. A method of separating benzol from hydrocarbon gases, consisting in evaporating a refrigerant under increasing partial pressures of refrigerant and over a range of increasing subatmospheric temperatures into an inert gas, grad'-.

flow heat-exchange with said inert gas with said refrigerant evaporating thereinto under said increasing partial pressures, and introducing liquid toluol into said hydrocarbon gases at the commencement of said cooling.

5. A method of separating benzol from hydrocarbon gases as defined in claim 3, in which said hydrocarbon gases are preccoled by upward contra-flow heat-exchange with escaping cooled hydrocarbon gases prior to being cooled by contraflow heat-exchange with said inert gas and refrigerant.

6. A method of separating benzol i'rom hydrocarbon gases as defined in claim 4, in which said hydrocarbon gases are preccoled by upward contra-flow heat-exchange with escaping cooled hy- I drocarbon gases prior to being cooled by contraflow heat-exchange with said inert gas and reirigerant. r

'7. A method 01 separating benzol from hydrocarbongases, consisting in evaporating a refrigerant under increasing partial pressures of refrigerant and over a range of increasing subatmospheric temperatures into an inert gas, gradually'cooiing said hydrocarbon gases by contraflow heat-exchangewith said inert gas with said refrigerant evaporating thereinto under said increasing partial pressures, collecting benzol condensed from said hydrocarbon gases, and spray-- ing some of said collected condensed benzol into said hydrocarbon gases at the commencement of said cooling.

-8. A method of separating benzol from hydrocarbon gases as defined-in claim "I, in which said hydrocarbon gases are preccoled by upward contra-flow heat-exchange with escaping cooled hydrocarbon gases prior to being cooled by contra flow heat-exchange with said inert gas and refrigerant.

' GUIDO MAIURI'. 

